Complete Level 15 - The Good, the Bad and the Hungry

Complete Level 13 - Magnetic Personality

Defeat 100 enemies as the Thing

Complete Level 10 - That Sinking Feeling

Complete Level 8 - Juggernauts and Crosses

Smelt an iron ingot.

Construct one type of each tool (one pickaxe, one spade, one axe and one hoe).

Complete Level 6 - Red Head Detention

Construct a better pickaxe.

Use planks and sticks to make a hoe.

Punch a tree until the block of wood pops out.

Open your inventory.